Magnetic core



H.. F. M RELL 1,731,861

MAGNETIC CORE Oct. 15, 1929.

Filed April 5, 1929 VII'IY -Fig 3. ll Nickel fronflllo y. I'll-ll Silicon Stel.

Inventor Harrg FIXC Rell,

His 'Attorneg.

Patented Oct. 15, 1929 UNITED STATES PATENT OFFICE HARRY I. MORELL, OI PITTSFIELD, MASSACHUSETTS, ASSI GNOR TO GENERAL ELEC- TBIC COMPANY, A CORPORATION 01" mew YORK MAGNETIC CORE Application filed April 5,

My, invention relates to magnetic cores for electrical induction apparatus such as transformers, reactors and the like. Almost all magnetic cores for alternating current elec-- trical apparatus are formed of superposed sheets'or laminations of magnetic material, the laminations being insulated from each other to prevent excessive eddy currents. The magnetic material most extensively used has been silicon steel as this material has good magnetic characteristics which it retains indefinitely. Other magnetic materials havin high permeability, such as nickel iron alloys, have also been used in magnetic cores, the high permeability of these materials making them niore desirable in some cases than silicon steel, but the comparatively high cost of these materials has resulted in their .very limited use.

After either the silicon steel or other mag: netic material has been worked into sheets or laminations of the desired thickness, the sheets are annealed to reduce eddy current losses in the finished core. It has been found that the annealing process produces an oxide film or coating adhering to the surfaces of silicon steel laminations and that this film will provide satisfactory insulation between the laminations when assembled together in a core. Any film or coating, however,- which is produced on a magnetic laminatiomnot containing silicon is conductive, and when sucli material is used the necessary insulation has to be provided in some other way. This is usu- N ally done by enameling or japanning the surfaces of the individual laminations after they are annealed and before they are assembled.

i The additional expense for labor and material still further offsets the advantages of these highly permeable materials as compared with silicon steel and so still further limits their use. The general object oftlie present invention is to provide an improved magnetic core including both silicon steel laminations and laminations .of some more highly permeable material such as nickel iron alloy arranged so that the benefits of the su perior magnetic characteristics of the highly permeable material is secured without any necessary additional expense for insulation.

1929. Serial No. 352,834.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. 1 is a diagrammatic view of a transformer having a magnetic core constructed in accordance with the invention; Fig. 2 is an end view of the core shown in Fig. 1, and Fig. 3 is an enlarged detail view of a small section of Fig. 2.

The invention will be explained in connection with the transformer shownin Fig. 1, this transformer including a magnetlc core 10 (provided With primary and secondary win ings 11 and 12. As shown in Figs. 2 and 3, the core 10 is formed of superposed laminations of magnetic material which must be insulated from each other to prevent excessive eddy currents. Part of the laminations are of-silicon steel and part of them are of highly permeable materialsuch as nickel iron alloy as indicated in Fig. 3. Before being assembled, the laminations are annealed to improve their magnetic characteristics, the annealing often being done before thelaminations are cut or punched from the original larger sheets. The annealmg process produces a thin insulating oxide film or coating on each surface of each of the silicon steel laminations which effectively insulates it from adjacent laminations to prevent appreciable eddy currents between them.

It has been found, however, that any film or coating produced on the laminations of nickel iron alloy or other highly permeable material not containing silicon is conductive. Each of these laminations is therefore arranged in the core with a silicon steel lamination next to it on each side so that all the highly permeable laminations are insulated by the insulating films produced by the annealing process on the surfaces of the adjacent silicon steel laminations. The two kinds of laminations may be arranged alternately in the core as indicated in Fig. 3 in which case, and providing the laminations are all of the same thickness, the magnetic material in the core is half nickel iron alloy or other highly permeable material and half silicon steel. It will be obvious, however, that a smaller proportion of thedaminations may be of highly permeable material so long as each of them as an annealed silicon steel lamination with its insulating coating next to it on each side. It has been demonstrated that the benefits of the superior magnetic characteristics of the highly permeable laminations are secured in substantially direct proportion to the proportion of this material in the core.

The invention has been explained by describing and illustrating a particular arrangement of magnetic corelaminations but it will be apparent that changes may be made without departing from the spirit and scope of the-invention as covered by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In electrical induction apparatus, a magnetic core including superposed laminations, part of said laminations being of silicon steel and part of them being of highly permeable material substantially free of silicon, said laminations being annealed to improve their magnetic characteristics, whereby the surfaces of said silicon steel laminations are provided with insulating coatings, each of said highly permeable laminations being arranged with a silicon steel lamination next to it on each side.

2. In electrical induction apparatus, a magnetic core including superposed laminations, part of said laminations being of silicon steel and part of them being of highly permeable material substantially free of silicon, said laminations being annealed to improve their magnetic characteristics, whereby the surfaces of said silicon steel laminations are provided with insulating coatings, the highly permeable laminations being arranged next to silicon steel laminations and insulated therefrom by said coatings.

3. In electrical induction apparatus, a magnetic core including superposed silicon steel and nickel iron alloy laminations, said laminations being annealed to improve their magnetic characteristics, whereby the surfaces of said silicon steel laminations are provided with insulating coating, each of said nickel iron alloy laminations being arranged with a silicon steel lamination nextto it on each side.

4. In electrical induction apparatus, a magnetic core including superposed silicon steel and nickel iron alloy laminations, said laminations being annealed to improve their electrical characteristics, whereby the surfaces of said silicon steel laminations are provided with insulating coatings,,the nickel iron alloy laminations being arranged next to silicon steel laminations and insulated therefrom by said coatings. I

5. In electrical induction apparatus, a magnetic core including superposed annealed laminations, the surfaces of part of said laminations having insulating coatings produced by the annealing process, other laminations 

